1. Field of the Invention
This invention relates to electrostatic precipitators and, more particularly, to an electrostatic precipitator utilizing a particle charging stage followed by a particle collection stage, both of which utilize an inner electrode supported by a single mounting system and powered by a single power supply.
2. Description of the Prior Art
Many industrial processes discharge considerable amounts of atmosphere contaminants as particulates in the sub-micron range. This type of particulate is most difficult to control. Fine particulate emission is becoming the major source of air pollution since the large particulate problems have been easier to bring under control.
Currently, there are three basic approaches to the problem of handling sub-micron size particulates in contaminated gases. The first basic approach is the traditional electrostatic precipitator system. However, the application of electrostatic precipitators to fine particulate control exhibits several inherent problems. One of these problems is contamination of the collector electrodes by the particles removed from the gas which causes the intensity of the electrostatic fields between the electrodes to decrease resulting in reduced particle collection efficiency. Another problem associated with electrostatic precipitators is high power consumption. In order to achieve a relatively high collection efficiency when the particles are less than two to five micron size, longer prior art electrostatic chambers or electrostatic fields of higher intensity must be employed. Longer electrostatic chambers and higher fields increase the current flow between the electrodes resulting in increased power consumption. Further, excessively long electrostatic chambers increase the cost of the equipment as well as the installation expense. Further, higher electrostatic fields also increase the precipitators sensitivity to electrode contamination.
The second basic prior art approach is the wet scrubbing approach which, as applied to the control of fine particulates, generally is of the high-energy venturi type. In order to capture sub-micron particulates in water droplets, however, large quantities of water must be injected and high relative velocities employed. Both of these factors increase the pressure drop of the system resulting in increased energy usage and hence operating cost.
The third basic prior art approach is the dry filter system. A problem with equipment of this type, however, is the temperature limitation of the filter elements, and the related problem of the high cost of reducing the temperature of the particle entrained gases upstream of the filter elements.
Efforts have been made to improve the efficiency of the above described approaches by electrostatically precharging the particulates upstream of the collecting system. These efforts have generally been unsuccessful due primarily to the lack of an effective mechanism for producing a continuous, sufficiently intense field to adequately charge the sub-micron sized particles. Furthermore, such systems generally utilize a charging device which is entirely separate from the collection device and hence require separate equipment, including power supplies, insulators, ducts, etc., for each device.